A ready-mixed concrete agitating truck is equipped with a concrete agitating drum for agitating and discharging ready-mixed concrete supplied from a hopper or the like. The agitating drum is driven by a hydraulic motor.
JP2000-272405A, published by the Japan Patent Office in 2000, proposes a hydraulic drive circuit for such a concrete agitating drum.
In this hydraulic drive circuit, the hydraulic motor is supplied with pressurized oil from a variable capacity hydraulic pump via a connection switch-over valve. The connection switch-over valve has a function to select a direction in which the pressurized oil discharged from the variable capacity hydraulic pump is supplied to the hydraulic motor as well as to shut off supply of the pressurized oil to the hydraulic motor. The concrete agitating drum rotates in a normal direction or a reverse direction according to an operation of the connection switch-over valve by an operator of the ready-mixed concrete agitating truck. Further, the concrete agitating drum stops rotating when the operator switches the connection switch-over valve to an operation-stop section.
The variable capacity hydraulic pump varies a pump discharge flow rate in response to an action of an actuator. The actuator is responsive to a discharge pressure of the pump. A load sensing valve regulates the pump discharge pressure and supplies a regulated pressure to the actuator, thereby maintaining a differential pressure between the discharge pressure of the hydraulic pump and a load pressure of the hydraulic motor at a constant value. Keeping the differential pressure constant means that the flow rate of the pressurized oil supplied from the hydraulic pump to the hydraulic motor is maintained at a constant flow rate. As a result, even when the rotation speed of the hydraulic pump, which is driven by an internal combustion engine, varies, the rotation speed of the agitating drum does not vary.